MEMS device

ABSTRACT

Provided is a MEMS device. The MEMS device includes: substrate having back cavity passing therethrough; diaphragm connected to the substrate and covers the back cavity, the diaphragm comprises first and second membranes, and accommodating space is formed between the first and second membranes; supports arranged in the accommodating space, and opposite ends of the support are connected to the first and second membranes; counter electrode arranged in the accommodating space, the first and second membranes each include conductive and second regions, the second region is formed by semiconductor material without doping conductive ions. Through design of the first and second membranes as the first region and the second region, respectively, the second region is formed by semiconductor material without doping conductive ions, and the first region is formed by doping conductive ions in the semiconductor material, so that the compliance performance is improved and not at risk of delamination.

TECHNICAL FIELD

The present disclosure relates to the technical field of micro electromechanical system (MEMS), in particular to a MEMS device.

BACKGROUND

In the related art, a microphone with a double-membrane structure hasbeen developed and produced. The microphone has two membranes onopposite sides of the counter electrode. This creates a sealedaccommodating space between the two membranes, which can have differentpressures compared to the external environment. If the pressure in theaccommodating space is reduced, this structure will significantly reduceself-noise associated with the counter electrode (a main noise source inMEMS microphones).

In the related art, the membrane is made of a conductive polysiliconconductor to act as an electrode, but this will adversely affectsensitivity of the microphone due to stray capacitance between the twomembranes.

SUMMARY

The purpose of the present disclosure is to provide a MEMS device tosolve the technical problems in the related art.

The present disclosure provides a MEMS device, including: a substratehaving a back cavity passing through the substrate; a diaphragmconnected to the substrate and covers the back cavity, the diaphragmincludes a first membrane and a second membrane arranged opposite toeach other, and an accommodating space is formed between the firstmembrane and the second membrane; a plurality of supports arranged inthe accommodating space, and opposite ends of each of the plurality ofsupports are respectively connected to the first membrane and the secondmembrane; and a counter electrode arranged in the accommodating spaceand spaced apart from the first membrane and the second membrane. Aplurality of ventilation slots are provided on the diaphragm along acircumferential direction thereof and are annularly spaced from eachother, the plurality of ventilation slots successively penetrate throughthe first membrane, the supports and the second membrane. The firstmembrane and the second membrane each includes a first region and asecond region, the first region extends from a center of the diaphragmtoward an edge of the diaphragm and does not extend to the ventilationslots. The first region is an electrode region, and the second region islocated at a circumferential outer side of the first region. The secondregion is formed by a semiconductor material without doping conductiveions, and the first region is formed by doping conductive ions in thesemiconductor material.

As an improvement, the MEMS device further includes a bonding padconnected to an external circuit and a conducting track connecting thefirst region to the bonding pad, the conducting track is arrangedavoiding the plurality of ventilation slots.

As an improvement, the first membrane includes a plurality of firstprotrusions protruding toward the accommodating space, and the secondmembrane includes a plurality of second protrusions protruding towardthe accommodating space, and the plurality of first protrusions and theplurality of second protrusions are connected by the supports.

As an improvement, a plurality of through holes are provided on theelectrode region, and the plurality of through holes, the plurality offirst protrusions and the plurality of second protrusions are inone-to-one correspondence.

As an improvement, the supports each include a plurality of supportmembers arranged concentrically, and the plurality of support membersare spaced along a radial direction of the diaphragm with a center ofthe diaphragm regarded as the center; and each of the plurality ofsupport members is composed of a plurality of first sectionsconcentrically arranged, the plurality of first sections are arranged atintervals, and a first notch is formed between two adjacent ones of theplurality of first sections.

As an improvement, positions of the first notches in two adjacent one ofthe plurality of support members are in a one-to-one correspondence, andarc lengths of the first notches increase along the radial direction ofthe diaphragm.

As an improvement, in at least one of the plurality of support membersclose to the edge of the diaphragm, the first sections is each composedof a plurality of second sections concentrically arranged, the pluralityof second sections are arranged at intervals, and a second notch isformed between two adjacent ones of the plurality of second sections.

As an improvement, the plurality of first sections and the plurality ofsecond sections are each an arc section.

Compared with the related art, the present disclosure configures thefirst membrane and the second membrane as a first region and a secondregion, respectively, and the first region avoids the position of theventilation slots, so that the first region can be positioned in themovement of the diaphragm at a position that can most effectivelygenerate electrical signals, thereby increasing the sensitivity of themicrophone. In addition, the second region is formed by a semiconductormaterial without doping conductive ions, and the first region is formedby doping conductive ions in the semiconductor material, so that thecompliance performance is improved and not at risk of delamination.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an isometric view of an MEMS device according to an embodimentof the present disclosure;

FIG. 2 is a top view of an MEMS device according to an embodiment of thepresent disclosure;

FIG. 3 is a schematic view showing an installation position of anelectrode region according to an embodiment of the present disclosure;

FIG. 4 is a schematic structural view of support members according to anembodiment of the present disclosure; and

FIG. 5 is a schematic diagram showing cooperation between an electroderegion and a support according to an embodiment of the presentdisclosure.

REFERENCE SIGNS

-   -   10—base,    -   11—back cavity;    -   20—diaphragm,    -   21—electrode region,    -   211—through hole,    -   22—first membrane,    -   221—first protrusion,    -   23—second membrane,    -   231—second protrusion,    -   24—accommodating space,    -   25—ventilation slot,    -   26—first region,    -   second region,    -   30—support,    -   31—support member,    -   32—first arc section,    -   33—first notch,    -   34—second arc section,    -   35—second notch,    -   40—counter electrode,    -   50—conducting track.

DESCRIPTION OF EMBODIMENTS

Embodiments described below with reference to the drawings areexemplary, and are only used to explain the present disclosure, whichshall not be construed as limiting the present disclosure.

As shown in FIGS. 1-3 , FIG. 1 is an isometric view of an MEMS deviceaccording to an embodiment of the present disclosure; FIG. 2 is a topview of an MEMS device according to an embodiment of the presentdisclosure; and FIG. 3 is a schematic view showing an installationposition of an electrode region according to an embodiment of thepresent disclosure. An embodiment provides a MEMS device, which includesa substrate 10, a diaphragm 20, a support 30, and a counter electrode40.

A back cavity 11 passes through the substrate 10. The inner contoursurface of the back cavity 11 may be a circular slot structure.

The diaphragm 20 is connected to the substrate 10 and covers the backcavity 11. The diaphragm 20 includes a first membrane 22 and a secondmembrane 23 that are arranged opposite to each other. In thisembodiment, the first membrane 22 and the second membrane 23 are bothconcentric circular structures. A predetermined gap is maintainedbetween the first membrane 22 and the second membrane 23 to form anaccommodating space 24. The first membrane 22 is located in an upperportion as shown in FIG. 1 , and the second membrane 23 is located belowthe first membrane 22.

The support 30 is arranged in the accommodating space 24, and oppositeends of the support 30 are respectively connected to the first membrane22 and the second membrane 23. The function of the support 30 is to keepthe first membrane 22 and the second membrane 23 flat, or at leastlimit/control the bending/deformation of the first membrane 22 and thesecond membrane 23 between the supports 30. Therefore, the firstdiaphragm 22 and the second membrane 23 can be prevented from beingfolded with each other when the sealed volume of the accommodating space24 is at a decreased atmospheric pressure and the outside is at anambient atmospheric pressure.

The counter electrode 40 is arranged in the accommodating space 24 in asuspended state. Generally, there is no contact between the counterelectrode 40 and the first membrane 22 and the second membrane 23, andthere is no mechanical coupling between the counter electrode 40 and thesupport member 31. It is appreciated that, in this context, the term“loop member” may refer to any member that forms a loop, for example acircular ring, a rounded square or rectangle or the like. The specificshape is not limited herein. A first capacitor is formed between thefirst membrane 22 and the counter electrode 40, and a second capacitoris formed between the second membrane 23 and the counter electrode 40.In response to the pressure applied to the first membrane 22 and thesecond membrane 23, the first membrane 22 and the second membrane 23 aremovable relative to the corresponding counter electrode 40, therebychanging the distances between first membrane 22 and the second membrane23 relative to the corresponding counter electrode 40. As a result, thecapacitance is changed to output an electrical signal accordingly.

In the present disclosure, the first membrane 22 and the second membrane23 both includes a first region 26 and a second region 27. For example,the first region 26 refers to an electrode region 21 on the secondregion 27. The electrode region 21 refers to the portion inside thesolid circle shown in FIG. 2 . The second region 27 is formed by asemiconductor material without doping conductive ions, and the firstregion 26 is formed by doping conductive ions in the semiconductormaterial, so that the compliance performance is improved and thus is noteasily peeled off. The electrode region 21 is connected to a bonding padby a conducting track 50 and the bonding pad is connected to an externalcircuit, so that the electrode region 21 can be positioned at a positionwhere the movement of the diaphragm 20 can be most effectively convertedinto electrical signals, so as to increase the sensitivity of themicrophone.

Referring to FIGS. 4-5 , FIG. 4 is a schematic structural diagram ofsupport members according to an embodiment of the present disclosure,and FIG. 5 is a schematic diagram showing cooperation between anelectrode region and a support according to an embodiment of the presentdisclosure. In the present embodiment, the electrode region 21 is also awafer structure. The electrode region 21 is arranged concentrically inthe middle of the diaphragm 20. In this embodiment, the circumference ofthe diaphragm 20 is connected to the substrate 10. Its deflectionpresents a parabolic shape being the largest at the center of thediaphragm 20 and decrease to zero at the edge.

In the present embodiment, the first membrane 22 and the second membrane23 are both provided with a ventilation slot 25. Optionally, theventilation slot 25 successively penetrates through the first membrane22, the supports 30 and the second membrane 23. That means a vent isprovided between the first membrane 22 and the second membrane 23.Therefore, the compliance of the membrane in the area where theventilation slot 25 is located can be significantly increased. Forexample the ventilation slots 25 may only be provided at periphery ofthe diaphragm 20. Several ventilation slots 25 may be located in thecircumferential area of the electrode region 21 at an intervals. Theventilation slots 25 on the first membrane 22 and the second membrane 23may have the same or different size and shape, which is not limitedherein.

Since the sensitivity of the microphone is determined by the ratio ofchange of the capacitance relative to the pressure, an electrode region21 is provided on the diaphragm 20 at a position where movement of thediaphragm is most intense, i.e. the middle portion of the diaphragm 20.The electrode region 21 is not provided at the edge of the diaphragm 20.Therefore, the parasitic capacitance between the first membrane 22 andthe second membrane 23 can be decreased, and the sensitivity of themicrophone can be increased accordingly.

In the present embodiment, as shown in FIG. 3 , the diaphragm 20 has acorrugated structure. The first membrane 22 includes a plurality offirst protrusions 221 protruding toward the accommodating space 24, andthe second membrane 23 includes a plurality of second protrusions 232protruding toward the accommodating space 24. The electrode region 21 isprovided with a plurality of through holes 211. The plurality of throughholes 211, the plurality of first protrusions 221 and the plurality ofsecond protrusions 232 are in one-to-one correspondence. The innercontour surface of the through hole 211 is adapted to the outer contoursurfaces of the first protrusion 221 and the second protrusion 232.

The support 30 is connected to the first protrusion 221 and the secondprotrusion 232. The first membrane 22 and the second membrane 23 areclose to each other at the support 30, at which position the capacitanceis the highest, and the through hole 211 is provided at the position ofthe electrode region 21 corresponding to the support 30. As a result,the electrode region 21 avoids the areas of the first protrusion 221 andthe second protrusion 232.

For example, the shapes and sizes of the first protrusions 221 and thesecond protrusions 232 are the same to form regular corrugations, sothat the stress distribution on the entire diaphragm 20 is uniform, andat the same time, it is advantageous for the forming process. Thecross-section of the first protrusion 221 and the second protrusion 232in the direction perpendicular to the diaphragm 20 may be a regularshape of rectangular, trapezoidal, or triangular, and the angle of theinclined surface of the first protrusion 221 and the second protrusion232 is greater than 0°, and less than or equal to 90°. Alternatively,the cross-section may be a irregular shape such as a rounded rectangleor a polygon. Those skilled in the art can understand that thecross-section of the first protrusion 221 and the second protrusion 232in the direction perpendicular to the diaphragm 20 can be either regularor irregular, which is not limited herein.

The first protrusion 221 and the second protrusion 232 together form acorrugation structure of the diaphragm 20, so that the diaphragm 20 canhave decreased tensile stress, due to the fact that the corrugatedstructure allows a decrease of the tensile stress in the diaphragm. Inaddition, the formed diaphragm 20 has a smaller size. Due to thedecreased internal stress, the stiffness of the diaphragm 20 is reduced,which effectively increases the mechanical sensitivity of the MEMSdevice.

Referring to FIG. 4 , the support 30 includes a support member 31arranged concentrically, and a plurality of support members 31 arearranged at intervals along the radial direction of the diaphragm 20with the center of the diaphragm 20 as the center.

The support member 31 may be an integral wall-shaped structure, or itmay be provided with a cavity, and the cavity may be filled with afilling material. The filling material may be an oxide, such as siliconoxide or the like. Alternatively, the cavity may be empty. Slots canalso be provided in the cavity to allow air from the externalenvironment or etching solution to enter the cavity to release thefilling material, thereby increasing the compliance of the firstmembrane 22 and the second membrane 23, and reducing the inter-platecapacitance between the first membrane 22 and the second membrane 23.

The support member 31 may be integrally formed with one of the firstmembrane 22 and the second membrane 23. Alternatively, after the firstmembrane 22 and the second membrane 23 are assembled together, a supportmember 31 is formed therebetween.

In the present embodiment, each support member 31 is composed of aplurality of concentrically arranged first arc sections 32. The counterelectrode 40 is provided with a via hole corresponding to the first arcsection 32 for the support member 31. The cross-section of the first arcsection 32 may be an arc structure, the inner diameters of the pluralityof first arc sections 32 in the same support member 31 are all the same,and the plurality of first arc sections 32 are arranged at intervals. Afirst notch 33 is formed between two adjacent first arc sections 32, andthe larger first arc section 32 is used to support the first membrane 22and the second membrane 23, so that the adjacent first arc sections 32have larger spacing therebetween, so as to solve the problem that thecounter electrode 40 requires a large amount of via holes. The design ofthe counter electrode 40 and the design of the support member 31 areseparately achieved. A first arc section 32 is much larger than thesmall pillars of the related art, which makes the pillar structurehaving the same aspect ratio become much taller. Therefore, it ispossible to use a thicker counter electrode 40, and allow for a morestiff structure, which can significantly improve the stability andreliability of the device.

In addition, for at least one support member 31, the first arc section32 is formed by the concentrically disposed second arc sections 34. Eachsecond arc section 34 cross-section has the same arc shape. In the samefirst arc section 32, the inner diameters of the second arc sections 34are all the same. The second arc sections 34 are arranged at intervals,and a second notch 35 is formed between two adjacent second arc sections34. There is no need to provide a via hole at the second notch 35,thereby increasing the rigidity of the counter electrode 40.

In the present embodiment, for the four support members 31 close to theedge of the diaphragm 20, the first arc section 32 consists of twoconcentrically arranged second arc sections 34. A second notch 35 isformed between the two arc second sections 34, and the second notch 35is located in the middle of the first arc section 32. Those skilled inthe art can understand that, the number and position of the second arcsections 34 included in a first arc section 32 may vary according to theactual situation, which is not limited herein.

With reference to FIG. 4 , the first notches 33 in the two adjacentsupport members 31 are in one-to-one correspondence. Along the radialdirection of the diaphragm 20, the arc lengths of first notches 33 inthe support members 31 gradually increase. Since there is no need toprovide a via hole at the position corresponding to the first notch 33,the rigidity of the counter electrode 40 can be further increased.

The structure, features, and effects according to the present disclosureare described in detail above based on the embodiments shown in thedrawings. The above are only preferred embodiments of the presentdisclosure. However, the above embodiment do not limit the scope of thepresent disclosure. Any changes or equivalent embodiments which still donot exceed the concept covered by the specification and illustrationsshould fall within the protection scope of the present disclosure.

What is claimed is:
 1. A micro electro mechanical system (MEMS) device,comprising: a substrate having a back cavity passing through thesubstrate; a diaphragm connected to the substrate and covers the backcavity, wherein the diaphragm comprises a first membrane and a secondmembrane arranged opposite to each other, and an accommodating space isformed between the first membrane and the second membrane; a pluralityof supports arranged in the accommodating space, and opposite ends ofeach of the plurality of supports are respectively connected to thefirst membrane and the second membrane; and a counter electrode arrangedin the accommodating space and spaced apart from the first membrane andthe second membrane, wherein a plurality of ventilation slots areprovided on the diaphragm along a circumferential direction thereof andare annularly spaced from each other, the plurality of ventilation slotssuccessively penetrate through the first membrane, the supports and thesecond membrane, the first membrane and the second membrane eachcomprises a first region and a second region, the first region extendsfrom a center of the diaphragm toward an edge of the diaphragm and doesnot extend to the ventilation slots, the first region is an electroderegion, the second region is located at a circumferential outer side ofthe first region, and the second region is formed by a semiconductormaterial without doping conductive ions, and the first region is formedby doping conductive ions in the semiconductor material.
 2. The MEMSdevice according to claim 1, further comprising a bonding pad connectedto an external circuit and a conducting track connecting the firstregion to the bonding pad, wherein the conducting track is arrangedavoiding the plurality of ventilation slots.
 3. The MEMS deviceaccording to claim 1, wherein the first membrane comprises a pluralityof first protrusions protruding toward the accommodating space, and thesecond membrane includes a plurality of second protrusions protrudingtoward the accommodating space, and the plurality of first protrusionsand the plurality of second protrusions are connected by the supports.4. The MEMS device according to claim 3, wherein a plurality of throughholes are provided on the electrode region, and the plurality of throughholes, the plurality of first protrusions and the plurality of secondprotrusions are in one-to-one correspondence.
 5. The MEMS deviceaccording to claim 4, wherein in at least one of the plurality ofsupport members close to the edge of the diaphragm, the first sectionsis each composed of a plurality of second sections concentricallyarranged, the plurality of second sections are arranged at intervals,and a second notch is formed between two adjacent ones of the pluralityof second sections.
 6. The MEMS device according to claim 5, wherein theplurality of first sections and the plurality of second sections areeach an arc section.
 7. The MEMS device according to claim 1, whereinthe supports each comprise a plurality of support members arrangedconcentrically, and the plurality of support members are spaced along aradial direction of the diaphragm with a center of the diaphragmregarded as the center; and each of the plurality of support members iscomposed of a plurality of first sections concentrically arranged, theplurality of first sections are arranged at intervals, and a first notchis formed between two adjacent ones of the plurality of first sections.8. The MEMS device according to claim 7, wherein positions of the firstnotches in two adjacent one of the plurality of support members are in aone-to-one correspondence, and arc lengths of the first notches increasealong the radial direction of the diaphragm.